Constructors??? what's the point

So i haven't figured out what the point of constructors are i am just learning C++ and am seriously having trouble with it, i do not get why...well i kind of get default constructors because it initializes the variables but what about a constructor with arguments and the member function

>>ok so i'll always need a default constructor even when i add other constructors

You can do both at the same time using default parameters, this is very common. For example, consider this simple class that represents a 2D vector:

class Vector2D {
public:
double x,y; //two data members to hold the x and y coordinates.
//you can have a constructor that takes the two coordinates to initialize the object with,
// by providing default parameters ("= 0.0"), the constructor can also be called with no parameters
// in which case they will have values (0.0,0.0)
Vector2D(double aX = 0.0, double aY = 0.0) : x(aX), y(aY) { };
};

The above is very useful to provide both a parametrized constructor and a default constructor at the same time, also making it explicit what the default values are.

As mentioned above, the main use of constructors is object initialization. You may think that this is not an important job, but
consider this -> You want to create a vector of 10 vectors of 10 ints and you want to assign the value 25 to all of them (the ints).

However, this is not the only use of constructors. Another thing you
can do with them is impose limitations on the ways your objects can
be created. There are cases where you want to disable copying for
your objects (because, let's say, you don't want to share ownership of
a resource). A special kind of constructor, called the copy constructor,
is invoked when you create a new object from an existing one. If you
make this constructor private, you make your objects non-copyable
(well, you also have to make the assignment operator private).

A real world example are the ostream and istream classes. Try to make a copy of
cout -> ostream cout_copy(cout); or cin -> istream cin_copy(cin); You can't. And what does the compiler say? error: 'std::ios_base::ios_base(const std::ios_base&)' is private within this context... Or something like that.

I have a 2d matrix with dimension (3, n) called A, I want to calculate the normalization and cross product of two arrays (b,z) (see the code please) for each column (for the first column, then the second one and so on).
the function that I created to find the ...

Write a C program that should create a 10 element array of random integers (0 to 9). The program should total all of the numbers in the odd positions of the array and compare them with the total of the numbers in the even positions of the array and indicate ...